A charging device has a charging unit and a control unit. The charging unit charges a battery pack the battery pack being either a first type or a second type of battery pack. The first type of battery pack includes a single battery cell or a first plurality of battery cells connected in series. The second type of battery pack includes a single battery unit or a second plurality of battery units connected in series. Each battery unit includes at least two battery cells connected in parallel. The control unit controls the charging unit to control at least one of a charging current flowing through the battery pack and a charging voltage applied across the battery pack, depending on the battery pack to be charged.